In a typical automotive air conditioning system, refrigerant is circulated through an evaporator core located at the front of the passenger compartment to cool air en route to the compartment. The evaporator core has a plate-and-fin construction formed of a stack of elements individually stamped from aluminum alloy sheet stock and brazed into an integral structure. Aluminum alloy is preferred because it has low specific gravity and high thermal transfer properties, and also because the evaporator may be fashioned from readily available sheet stock by convenient operations such as stamping and brazing.
The plate-and-fin design of the evaporator core provides numerous air passages for maximum contact with heat exchanger surfaces. During air conditioning operation, moisture condenses within the air passages of the evaporator core and promote the growth of microorganisms, which, if excessive, may produce an unpleasant odor or otherwise affect passenger comfort. U.S. Ser. No. 360,681, assigned to the assignee of the present invention, describes an aluminum evaporator core coated with a metallic copper plate to inhibit microbial growth. Condensate collecting in the air passages tends to be slightly acidic and reacts with the copper to produce cupric ions. The cupric ionst in turn, dissolve in the condensate and inhibit biological growth. A potential corrosion problem arises where the substrate aluminum comes in physical and/or electrical contact with the copper plate.
U.S. Ser. No. 07/572,649 assigned to the assignee of the present invention, describes an evaporator core further comprising a biocidal fixture attached to the heat exchanger upstream face. The fixture comprises a carrier formed of an electrically nonconductive polymer and a metallic copper plate deposited on the surface of the carrier spaced apart from the heat exchanger. During air conditioning operations, condensate collecting on the copper surfaces reacts with the copper to generate cuptic ions that disperse in the condensate to inhibit biological growth within the heat exchanger passages. However, it is desirable to inhibit or resist growth of microorganisms without the need to attach a separate fixture to the core.
Therefore, it is desirable to have an improved evaporator core which is resistant to growth of microorganisms, and easy to use and economical; and a method for making such an improved evaporator core.